This undated file identification photo released Sept. 12, 2010, by Vermont State Police shows Pat O’Hagan, 78, of Sheffield. Hagan disappeared from her home in September 2010. Her body was found nearly a month later by hunters in a remote area 10 miles away.

BURLINGTON — Three men have been implicated in the September 2010 killing of a 78-year-old grandmother during a botched robbery at her home during which she was sexually assaulted before being shot in the head, say federal court documents filed in connection with another case.

No charges have been filed in connection with the killing of Mary “Pat” O’Hagan, who was missing for about three weeks before her body was found in Wheelock.

The suspects, who are related, provided different reasons for the killing, including robbery and that O’Hagan had learned about methamphetamine being cooked at an abandoned house next door to her home, the federal court documents said.

The court documents say the three men — Richard E. Fletcher, 26; his brother, Keith J. Baird, 32; and Fletcher’s cousin Michael Norrie, 22, all of Sheffield — have been implicated in the killing. All three are in federal or state custody on charges unrelated to the killing of O’Hagan.

“After a thorough investigation, Vermont authorities have concluded that Fletcher, accompanied by two male relatives, participated in the crime leading to the killing and disposal of the body,” prosecutors wrote in a sentencing memorandum for Fletcher who is facing almost 16 years in prison on charges of sexual exploitation of a minor.

The Burlington Free Press reported none of the attorneys for the three men could be reached for comment.

Norrie was first publicly linked to the case in January 2011 when he made incriminating statements to federal agents investigating another case. The accusations against Fletcher and Baird became public Monday in documents submitted for Fletcher’s upcoming sentencing.

State prosecutors have not said why no charges have been filed in connection with O’Hagan’s death.

Assistant Vermont Attorney General Cindy Maguire, chief of the criminal division, said the standard for a criminal trial in state court and a federal sentencing is different.

“It is still a pending criminal investigation. We are not going to comment further with respect to the state’s case,” she said.